ci: fix tests in node 8 & 9

fix nyc version to 14.1.1 when running tests in node 8 or node 9. nyc 15.x requires a version of yargs package version requires node >=10.

fixes #108

Author: carpasse

.github/workflows/ci.yml

@@ -75,11 +75,11 @@ jobs:
 
         - name: Node.js 8.x
           node-version: "8.17"
-          npm-i: [email protected]
+          npm-i: [email protected] [email protected]
 
         - name: Node.js 9.x
           node-version: "9.11"
-          npm-i: [email protected]
+          npm-i: [email protected] [email protected]
 
         - name: Node.js 10.x
           node-version: "10.24"